This invention relates to novel sealants and adhesives containing highly functionalized selectively hydrogenated block copolymer of vinyl aromatic hydrocarbons and conjugated dienes. More particularly, it relates to sealants and adhesives having improved shear adhesion failure temperatures and slump resistance.
U.S. Pat. No. 4,578,429 describes selectively hydrogenated block copolymers modified with acid compounds or derivatives thereof. The patent describes making ABA block copolymers wherein the A blocks are vinyl aromatic hydrocarbons and the B blocks are conjugated dienes, selectively hydrogenating them to hydrogenate primarily the B blocks and then functionalizing them by free radical grafting with monomers containing functional groups or their derivatives such as carboxylic acid groups and their salts, anhydrides, esters, imide groups, amide groups, acid chloride and the like in addition to having at least one point of unsaturation in the monomer. The polymers produced are said to be thermally stable, have a low residual unsaturation, excellent in appearance characteristics, melt-flow characteristics and mechanical properties such as tensile strength and impact resistance, and have excellent transparency. The grafted polymers are said to contain from 0.02 to 20 weight percent of the grafted monomer.
Commercial products of this type have been available for several years. These commercial products contain slightly less than two percent maleic anhydride grafted on to a hydrogenated styrene butadiene styrene block copolymer. They have been proven to be useful in sealants and adhesives. However, sealants using such polymers have not been used successfully at high service temperatures such as 55-60.degree. C. because the sealant has a tendency to fail under shear stress at that temperature. Sealants made from these polymers also have a tendency to slump unacceptably at elevated temperatures, e.g. 64-70.degree. C. Thus, it would be advantageous to provide a functionalized selectively hydrogenated block copolymer having the advantages of the functionalized block copolymers described in U.S. Pat. No. 4,578,429 with the additional advantage of being useful at high service temperatures, i.e., up to 80.degree. C.
Unfunctionalized selectively hydrogenated and unhydrogenated block copolymer of vinyl aromatic hydrocarbons and conjugated dienes have been proven to be difficult to emulsify. The aforementioned commercially available maleic anhydride functionalized block copolymers are much easier to emulsify but more than one part of a surfactant per 100 parts rubber is required. Since surfactants negatively affect the adhesive properties of such emulsions, it would advantageous to be able to provide a stable emulsion of a functionalized block copolymer which requires little or no surfactant.